This invention pertains to the field of solid waste materials and more particularly to a method of disposal of toxic particulate material by encapsulation in an asphalt emulsion.
Certain industrial processes, such as the combustion of waste solids, produce a fly ash which is environmentally hazardous due to the presence of toxic elements such as lead. Such fly ash cannot be disposed of in a standard landfill due to the leaching of the toxic material into the water table. Even where there is a material which renders the waste resistant to leaching, landfill sites are becoming scarce and expensive.
One method of disposing of waste fly ash which has been used in the past where the level of toxic elements in the fly ash has been sufficiently low has been the addition of the fly ash as a filler in asphalt concrete pavement or blacktop. This method of disposal is unsuitable for fly ash having high levels of toxic elements since some leaching of the toxic elements still occurs.
U. S. Pat. No. 4,623,469 issue Nov. 18, 1986 to Chem-Technics, Inc. discloses a method of disposing of hydrophillic liquid and semi-liquid waste by mixing the waste liquid and asphalt to generate a solid hydrophobic mass which can be disposed of in a landfill. According to this method, the ionic charge of the waste counter ions is determined and an emulsified asphaltic suspension having a particle charge opposite to the ionic charge of the waste counter ions is selected. Enough of the selected asphaltic emulsion is added to the waste liquid to coalesce into a solid hydrophobic mass. The mixture is allowed to set and cure to a solid state. This method, however, uses valuable landfill space, and the end product is not commercially useful.
An asphalt emulsion, or emulsified asphalt, is an emulsion of fine droplets of asphalt cement or bitumen in water. The emulsion is stabilized by the presence of an emulsifying agent, such as a detergent. Depending on the emulsifying agent used, such emulsions are either anionic, having negatively charged asphalt globules, or cationic, having positively charged asphalt globules. Such emulsions are commercially available for a number of uses. One such use is to form an asphalt emulsion slurry seal which is a mixture of emulsified asphalt, fine aggregate and mineral filler with water to produce a slurry. When dried by water evaporation, the slurry becomes a thick, jelly-like coating material which is applied wet much like a paint to coat pavement, driveways and the like.
For use as a coating for pavement, or for coating layers of garbage in garbage dumps, or similar applications, it is important that the asphalt coating be quick setting to minimize the period when the roadway is not in use, or the period before the next layer of garbage can be laid in the latter garbage dump application. In such quick-setting applications, the addition of substances such as cement which retard the setting of the asphalt emulsion is to be avoided.
There is therefore a need for a method of safely disposing of toxic particulate waste in a manner which is resistant to leaching yet does not require valuable landfill space and can be used commercially.